Western Flyer’s hybrid system

By Tom Keffer, Board President

With the renovation of Western Flyer, we had a number of choices of what to use for a propulsion system. We really wanted to do a pure electric vessel, but then reality intruded. This is a rapidly changing technology, but prices are still very high. We estimated that it would cost at least $1.2M to install the necessary batteries and motors, and whatever we came up with would likely be obsolete within 5 or 6 years. That’s a cost that we just couldn’t afford.

It would also come with a number of operational limitations. While it would be very green in a state such as California with its relatively low-carbon electrical grid, that would not be the case in Mexico, where we expect to spend up to a quarter of our time. There, the grid is largely coal and oil-fired, leading to total emissions that would actually be higher than a modern tier-four diesel!

So, we chose to do the next best thing: a diesel-electric hybrid. This is a system that is largely diesel-powered but can switch to electric mode for relatively brief periods of time. Besides being cleaner, a diesel-electric has several other advantages. The Western Flyer will have to hold research stations for long periods of time, which requires a slow-turning motor that reverses a lot, both of which diesels hate doing.  For a long-haul, cargo-carrying ship that’s not a problem — they just put the thing in gear in Yokohama and don’t take it back out until they reach Oakland — but, for us, who might be reversing hundreds of times in a day, it would be inefficient and mechanically troublesome. With a hybrid system, we can just switch to electric mode, allowing speeds from zero to full max 1850 RPM, in forward and reverse, with just a single control and no clutch engaging and disengaging.

Running a hybrid also opens up some very interesting research possibilities. When in electric mode, the boat, with its wooden hull and electric motor, will be extraordinarily quiet and less intrusive in near-shore environments. We wonder what scientists might be missing when approaching an area with a thumping diesel and a loud exhaust stack. We will be able to sit quietly in a patch of water for long periods of time, watching and observing.

The system we chose uses a traditional John Deere 6135 marine diesel (425 HP or 320 kW), mated to a Transfluid HM3350, manufactured in Italy. Looking a bit like the Starship Enterprise, the unit sits between the diesel and the gearbox. It has two 50 kW motors (the “warp drives”), which are engaged through a pinion gear and clutching mechanism when in electric mode. 

The Transfluid HM3350. The left end is mated to the diesel, the right end to the gearbox. The two cylinders on the right are the electric motors/generators.

With the 700 kWh of battery capacity on board, these motors will be able to drive Flyer at 3 knots for 6-8 hours, and at 8 knots for about 2-3 hours. Because the power take-offs (PTOs) are connected to the hybrid unit and the gearbox, the hydraulics can also be electrically powered, resulting in an ultra-quiet vessel.

When we’re done for the day, Flyer heads back to port, recharging the batteries through the same motors, now turned into generators. It takes about an hour to put an hour’s worth of electricity back into the batteries.

A look at aft end of the propulsion system

The output side of the hybrid unit is mated to a more traditional 6:1 Twin Disc reduction gear, and then to a 4” propshaft, which runs the length of the boat, then through a PYI dripless stuffing box. Finally, it all ends up with a 60” prop, pitched at 60”. 

While we will start with a relatively modest set of batteries, we imagine that as prices come down, we will be able to install more and more battery capacity, enabling longer and longer operational range as a pure electric vessel.

Sea trials are scheduled for May 2023. We are very excited to see what this system can do!

Read about the Western Flyer’s original engine, the Atlas-Imperial Diesel.

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